1. Field of the Invention
The invention relates to a vehicle for installing a cable in a ground formation, in particular in a seabed, comprising a frame, propulsion means, a cutter assembly for forming a trench and a guide for placing the cable in the trench. The invention also relates to the guide itself and to a method of temporarily interrupting the installation of a cable.
2. Brief Description of the State of the Art
Vehicles of this type are often referred to as “cable trenching machines” or simply “trenchers” and are known in the art.
WO 00/60178 discloses a method of forming a trench at sea on the seabed comprising the steps of providing an ROV (remotely operable vehicle) (2) capable of being operated underwater, providing a separate trenching skid (1) removably connectable to the ROV (2), connecting the trenching skid (1), possibly via an interface skid (3), to the ROV to form an operative trenching system (1, 2, 3), the connection being capable of being made while the trenching skid (1) is on the seabed, and operating the trenching system to form a trench underwater.
U.S. Pat. No. 5,722,793 discloses a method comprising the steps of using a self-propelled cable-burying tractor (1) remotely controlled via a flexible control umbilical (2) and provided with at least one drum (6) for a flexible cable (7), controlling said cable-burying tractor from a first location (5) in order to lay and bury the flexible cable as far as a first predetermined point (P1), controlling said cable-burying tractor beyond said first predetermined point from a second location (10), and continuing to lay and bury the flexible cable as far as a second predetermined point (P2), one of said locations being on land (5) while the other is a surface vessel (10). It is stated in U.S. Pat. No. 5,722,793 that this method is particularly suitable for laying and burying flexible cables such as optical cables, coaxial cables for analogue transmission, electrical cables and single or multiple flexible tubular ducts.
WO 2004/055276 discloses an apparatus for forming a trench (16) in the surface of the earth (15), for example a trench for energy lines, communication lines, etc., which apparatus comprises a frame (1) provided with propulsion means (2, 3), on which frame at least one trench forming device (5) is mounted. The trench-forming device (5) comprises at least one driveable drill bit (6), whose axis of rotation is oriented substantially parallel to the direction of movement of the apparatus during operation of the apparatus.
If the installation of a cable must be interrupted and the trencher hoisted, e.g. because of weather conditions or a malfunction of the trencher or the surface vessel from which the trencher is operated, the cable, which must, as a matter of course, remain on the seabed when the trencher is hoisted, is likely to slide into the trench and/or the trench is likely to cave in. Further, it will be difficult to locate the correct section of the cable and resume trenching.